Olefin polymerization catalysts containing triquinane ligands

ABSTRACT

A catalyst system useful for polymerizing olefins is disclosed. The catalyst system comprises an activator and an organometallic complex that incorporates a Group 3 to 10 transition metal and at least one chelating, dianionic triquinane ligand. The cis,syn,cis-triquinane framework is generated in three high-yield steps from inexpensive starting materials, and with heat and light as the only reagents. By modifying substituents on the triquinane ligand, polyolefin makers can control catalyst activity, comonomer incorporation, and polymer properties.

FIELD OF THE INVENTION

[0001] The invention relates to catalysts useful for olefinpolymerization. In particular, the invention relates to transition metalpolymerization catalysts that incorporate a chelating, dianionictriquinane ligand.

BACKGROUND OF THE INVENTION

[0002] While Ziegler-Natta catalysts are a mainstay for polyolefinmanufacture, single-site (metallocene and non-metallocene) catalystsrepresent the industry's future. These catalysts are often more reactivethan Ziegler-Natta catalysts, and they produce polymers with improvedphysical properties. The improved properties include narrow molecularweight distribution, reduced low molecular weight extractables, enhancedincorporation of α-olefin comonomers, lower polymer density, controlledcontent and distribution of long-chain branching, and modified meltrheology and relaxation characteristics.

[0003] Traditional metallocenes incorporate one or more cyclopentadienyl(Cp) or Cp-like anionic ligands such as indenyl, fluorenyl, or the like,that donate pi-electrons to the transition metal. Non-metallocenesingle-site catalysts, including ones that capitalize on the chelateeffect, have evolved more recently. Examples are 8-quinolinoxy or2-pyridinoxy ligands (see U.S. Pat. No. 5,637,660) and the bidentatebisimines of Brookhart (see Chem. Rev.100 (2000) 1169).

[0004] Recently, we described chelating bicyclic dianionic ligandsuseful for olefin polymerization catalysts (see copending U.S.application Ser. No. 09/907,180, filed Jul. 17, 2001). In thesecomplexes, one ligand chelates to the metal through two separate allylicanions, each of which is a 4-pi electron donor. Molecular modelingcalculations indicate that the steric and electronic environments ofthese ligands are comparable to those of conventional metalloceneligands. Their “open architecture” suggests that comonomer incorporationwill be facile. Triquinane or other tricyclic dianionic ligands are notdisclosed.

[0005] We also described earlier the use of Diels-Alder andphoto-chemical [2+2] cycloaddition reactions in tandem to make “cageddiimide” complexes (see copending U.S. application Ser. No. 09/691,285,filed Oct. 18, 2000). Conversion of a caged diketone to thecorresponding diimine, followed by preparation of a transition metalcomplex incorporating the neutral diimine ligand affords complexesuseful for olefin polymerization.

[0006] The tandem strategy was used by G. Mehta et al. (J. Am. Chem.Soc. 108 (1986) 3443) in a remarkable route to triquinane naturalproducts such as (±)-hirsutene and (±)-capnellene. The key to assemblingthese skeletons efficiently was recognizing that thecis,syn,cis-triquinane skeleton is available in three steps innear-quanitative yield (>80% overall) from inexpensive startingmaterials (p-benzoquinone and cyclopentadienes), and essentially nochemical reagents other than a reaction solvent (in addition to heat,and light):

[0007] In the example shown above, simple thermolysis of pentacyclicdiketones 3 and 4 gave only the cis,syn,cis-triquinane bis(enone)s 5 and6. After these pivotal, elegant steps, Mehta further elaborated thebis(enone)s to make the desired natural product, capnellene.

[0008] The polyolefins industry continues to need new polymerizationcatalysts. Unfortunately, the organometallic complexes are becomingincreasingly complicated and more expensive to manufacture. The industrywould benefit from ways to achieve a high level of molecular complexityin relatively few synthetic steps. The accessibility of a host ofinteresting triquinane skeletons invites polyolefin makers to exploretheir applicability outside the realm of natural products synthesis.Catalysts with advantages such as higher activity and better controlover polyolefin properties are within reach. Ideally, these catalystswould avoid the all-too-common, low-yield, multi-step syntheses fromexpensive, hard-to-handle starting materials and reagents.

SUMMARY OF THE INVENTION

[0009] The invention is a catalyst system useful for polymerizingolefins and a method for making it. The catalyst system comprises anactivator and an organometallic complex. The complex incorporates aGroup 3 to 10 transition metal and a chelating, dianionic triquinaneligand that is pi-bonded to the metal. The requiredcis,syn,cis-tricyclic framework is generated in high yield in threesteps from inexpensive starting materials, and with heat and light asthe only “reagents.” Further elaboration to a triquinane diene, adianionic ligand, and an organometallic complex incorporating theligand, are facile. By modifying substituents on the triquinane ligand,polyolefin makers can control catalyst activity, comonomerincorporation, and polymer properties.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Catalyst systems of the invention include an organometalliccomplex that contains a Group 3-10 transition metal. “Transition metal”as used herein includes, in addition to the main transition groupelements, elements of the lanthanide and actinide series. More preferredcomplexes include a Group 4 or a Group 8 to 10 transition metal.

[0011] The organometallic complex includes at least one chelating,dianionic triquinane ligand. The ligand “chelates” with the transitionmetal by bonding to it with two separate allylic bonds, each of which isa 4-pi electron donor. The ligand is “dianionic,” i.e., it has a netcharge of −2; each of two electron pairs generated by deprotonation isconjugated with a carbon-carbon double bond.

[0012] By “triquinane,” we mean a carbocyclic framework characterized bythree rings in which a central five-membered ring is cis,syn,cis-fusedto two additional five- or six-membered rings. Preferably, all of therings are five-membered. Thus, in an unsubstituted dianionic triquinane,all four bridgehead methine hydrogen atoms occupy the same face of thecentral five-membered ring. For example:

[0013] The triquinane framework can be substituted with other atoms thatdo not interfere with formation of the allylic dianion or incorporationof the dianion into a transition metal complex. For example, thetriquinane can be substituted with alkyl, aryl, halide, alkoxy,thioether, alkylsilyl, or other groups. Preferably, the framework ishydrocarbyl.

[0014] Preferred triquinane ligands have the general structure:

[0015] in which each R is independently hydrogen, halide, or C₁-C₃₀hydrocarbyl. Preferably, each R is a hydrogen.

[0016] The triquinane ligand is made by any suitable method. A preferredmethod utilizes tandem Diels-Alder and photochemical [2+2] cycloadditionreactions to generate a pentacyclic diketone, which is then converted toa triquinane diene. Double deprotonation generates the desired dianionicligand.

[0017] In one aspect, the invention is a method for making anorganometallic complex useful for olefin polymerization. In this method,a pentacyclic diketone such as 7 is first converted to a triquinanediene (e.g., 8) by methods that are detailed further below. Doubledeprotonation of the diene using a strong base gives a triquinanedianion such as 9. Reaction with a transition metal source gives anorganometallic complex (e.g., 10) that incorporates the chelating,dianionic triquinane ligand. Preferably, the pentacyclic diketone isproduced by reacting a cyclopentadiene and a p-benzoquinone, optionallyin the presence of an organic solvent, to produce a Diels-Alder adduct.The adduct is then preferably irradiated with light of a suitableenergy, optionally in the presence of a solvent and sensitizer, toeffect a [2+2] cycloaddition reaction to give the pentacyclic diketone.

[0018] For example:

[0019] As noted above, the pentacyclic diketone can be converted to a 5triquinane diene such as 8 by several methods. In one approach, thepentacyclic diketone is first heated to cause a [2+2] cycloreversionreaction to give a cis,syn,cis-triquinane bis(enone), e.g. 11. See Mehtaet al., J. Am. Chem. Soc. 108 (1986) 3443. For example:

[0020] Any suitable method is used to convert the bis(enone) to thetriquinane diene. In a two-step approach, the bis(enone) reacts with anarylhydrazine to produce an arylhydrazone. The arylhydrazone is thenreduced to the diene by reacting it with either an alkali metalcyanoborohydride (see R. Hutchins et al., J. Org. Chem. 40 (1975) 923)or catecholborane (G. Kabalka et al., J. Org. Chem. 41 (1976) 574). Inanother preferred method, the bis(enone) reacts with atrialkylhydrosilane in the presence of a Lewis acid to give thetriquinane diene in one step (see O. Dailey, Jr., J. Org. Chem. 52(1987) 1984. These strategies are summarized below. Note that either 8or 12 will yield the same dianion upon deprotonation:

[0021] In another preferred approach to making the triquinane diene, thepentacyclic diketone is first converted to a pentacyclic hydrocarbonsuch as 13 by modified Wolff-Kishner reduction (see Huang-Minlon, J. Am.Chem. Soc. 68 (1946) 2487). Heating promotes a [2+2] cycloreversionreaction to give the triquinane diene (e.g., 8):

[0022] As noted earlier, the “triquinane” framework can actuallyincorporate six-membered rings. These are conveniently introduced usingthe valuable “homologation” procedure with excess diazomethane. (Seegenerally J. March, Advanced Organic Chemistry, 2d ed. (1977) pp.997-998, and Example 41 of U.S. Pat. No. 4,855,322). By using thesynthetic strategies outlined earlier, the homologated product, e.g. 14,can be elaborated to an organometallic complex such as 15:

[0023] An advantage of the invention is versatility. By selecting theinitial Diels-Alder reactants judiciously, one can ultimately make awide variety of different chelating, dianionic triquinane complexes.This allows a skilled person to “fine tune” the catalyst to improve itsactivity or enable the preparation of polyolefins having a desirablemelt-flow index, molecular weight distribution, density, or otherproperty. A few examples:

[0024] 1. From a halogenated cyclopentadiene:

[0025] 2. From a halogenated p-benzoquinone:

[0026] 3. From other pentacyclic diketones:

[0027] In sum, the invention provides access to a wide variety ofcomplexes that incorporate chelating, dianionic triquinane ligands. Themethods discussed at length above are merely illustrative, and thoseskilled in the art will readily recognize or devise many alternativesynthetic methodologies.

[0028] Chelating dianionic triquinane ligands are made by doublydeprotonating the corresponding diene with a potent base according towell-known methods. Suitable bases include, for example, alkyllithiumcompounds (e.g., methyllithium or n-butyllithium), alkali metals (e.g.,sodium metal), alkali metal hydrides (e.g., potassium hydride), andGrignard reagents (e.g., methyl magnesium chloride or phenyl magnesiumbromide). Particularly preferred deprotonating agents are super-basicreagents prepared by the reaction of alkyllithium compounds and alkalimetal t-butoxides, as reported by Schlosser et al. (Angew. Chem., I.E.Engl. 12 (1973) 508) and Lochmann et al. (Tetrahedron Lett. (1966) 257).

[0029] Usually, about two equivalents of the deprotonating agent andabout one equivalent of the diene are used to produce the dianionicligand. Deprotonation can be performed at any suitable temperature,preferably at or below room temperature. While the deprotonationreaction can be performed at temperatures as low as −78° C. or below, itis preferred to perform this step at room temperature.

[0030] In addition to the dianionic triquinane ligand, theorganometallic complex may include additional labile anionic ligandssuch as halides, alkyls, alkaryls, aryls, dialkylaminos, or the like.Particularly preferred are halides, alkyls, and alkaryls (e.g.,chloride, methyl, benzyl).

[0031] Particularly preferred complexes have the structure:

[0032] in which M is a Group 4 transition metal and each X is a halide.

[0033] The catalyst system includes an activator. Suitable activatorshelp to ionize the organometallic complex and activate the catalyst.Suitable activators are well known in the art. Examples includealumoxanes (methyl alumoxane (MAO), PMAO, ethyl alumoxane, diisobutylalumoxane), alkylaluminum compounds (triethylaluminum, diethyl aluminumchloride, trimethylaluminum, triisobutyl aluminum), and the like.Suitable activators include acid salts that contain non-nucleophilicanions. These compounds generally consist of bulky ligands attached toboron or aluminum. Examples include lithiumtetrakis(pentafluorophenyl)borate, lithiumtetrakis(pentafluorophenyl)aluminate, aniliniumtetrakis(penta-fluorophenyl) borate, and the like. Suitable activatorsalso include organoboranes, which include boron and one or more alkyl,aryl, or aralkyl groups. Suitable activators include substituted andunsubstituted trialkyl and triarylboranes such astris(pentafluorophenyl)borane, triphenylborane, tri-n-octylborane, andthe like. These and other suitable boron-containing activators aredescribed in U.S. Pat. Nos. 5,153,157, 5,198,401, and 5,241,025, theteachings of which are incorporated herein by reference. Suitableactivators also include aluminoboronates—reaction products of alkylaluminum compounds and organoboronic acids—as described in U.S. Pat.Nos. 5,414,180 and 5,648,440, the teachings of which are incorporatedherein by reference.

[0034] The optimum amount of activator needed relative to the amount oforganometallic complex depends on many factors, including the nature ofthe complex and activator, whether a supported catalyst is used, thedesired reaction rate, the kind of polyolefin product, the reactionconditions, and other factors. Generally, however, when the activator isan alumoxane or an alkyl aluminum compound, the amount used will bewithin the range of about 0.01 to about 5000 moles, preferably fromabout 10 to about 500 moles, of aluminum per mole of transition metal,M. When the activator is an organoborane or an ionic borate oraluminate, the amount used will be within the range of about 0.01 toabout 5000 moles, preferably from about 0.1 to about 500 moles, ofactivator per mole of M.

[0035] The activator is normally added to the reaction mixture at thestart of the polymerization. However, when a supported catalyst systemis used, the activator can be deposited onto the support along with theorganometallic complex.

[0036] The organometallic complex is prepared according to methods thatare well known in the art. In general, the complexes are made bycombining the dianionic triquinane ligand with a transition metalsource. Any convenient source of transition metal can be used. Forexample, the complexes can be made from transition metal halides,alkyls, alkoxides, acetates, amides, or the like. A particularlyconvenient source of the transition metal is the transition metalhalide. For example, one can use titanium tetrachloride, zirconiumtetrachloride, vanadium(III) chloride-tetrahydrofuran complex(VCl₃(THF)₃), titanium (III) chloride-THF complex, chromium(III)chloride-THF complex, cobalt(II) chloride, nickel(II) bromide,platinum(II) chloride, palladium(II) chloride, lanthanum(III) chloride,titanium(III) acetate, or the like. Complexes can also be prepared fromsalts with labile groups, such as tetrakis(acetonitrile)palladium(II)bis(tetrafluoroborate).

[0037] The transition metal complexes are easy to make. Usually, thetransition metal source (halide, e.g.) is dissolved or suspended in anorganic solvent and the dianionic triquinane ligand is carefully addedat any desired temperature, preferably from about −78° C to about roomtemperature. Refluxing is used if needed to complete the reaction.Insoluble by-products, if any, can be removed by filtration, solventsare evaporated, and the transition metal complex is isolated, washed,and dried. The resulting complex can generally be used without furtherpurification.

[0038] The catalyst systems are optionally used with an inorganic solidor organic polymer support. Suitable supports include silica, alumina,silica-aluminas, magnesia, titania, clays, zeolites, or the like. Thesupport is preferably treated thermally, chemically, or both prior touse to reduce the concentration of surface hydroxyl groups. Thermaltreatment consists of heating (or “calcining”) the support in a dryatmosphere at elevated temperature, preferably greater than about 100°C., and more preferably from about 150 to about 600° C., prior to use. Avariety of different chemical treatments can be used, including reactionwith organo-aluminum, -magnesium, -silicon, or -boron compounds. See,for example, the techniques described in U.S. Pat. No. 6,211,311, theteachings of which are incorporated herein by reference.

[0039] The complex and activator can be deposited on the support in anydesired manner. For instance, the components can be dissolved in asolvent, combined with a support, and stripped. Alternatively, anincipient-wetness technique can be used. Moreover, the support cansimply be introduced into the reactor separately from the complex andactivator.

[0040] The loading of complex on the support varies depending upon anumber of factors, including the identities of the complex and thesupport, the type of olefin polymerization process used, the reactionconditions, and other concerns. Usually, the amount of complex used iswithin the range of about 0.01 to about 10 wt. % of transition metalbased on the amount of supported catalyst. A more preferred range isfrom about 0.1 to about 4 wt. %.

[0041] Catalyst systems of the invention are useful for polymerizingolefins. Preferred olefins are ethylene and C₃-C₂₀ α-olefins such aspropylene, 1-butene, 1-hexene, 1-octene, and the like. Mixtures ofolefins can be used. Ethylene and mixtures of ethylene with C₃-C₁₀α-olefins are especially preferred.

[0042] Many types of olefin polymerization processes can be used.Preferably, the process is practiced in the liquid phase, which caninclude slurry, solution, suspension, or bulk processes, or acombination of these. High-pressure fluid phase or gas phase techniquescan also be used. The process of the invention is particularly valuablefor solution and slurry processes.

[0043] The olefin polymerizations can be performed over a widetemperature range, such as about −30° C. to about 280° C. A morepreferred range is from about 30° C to about 180° C.; most preferred isthe range from about 60° C. to about 100° C. Olefin partial pressuresnormally range from about 15 psig to about 50,000 psig. More preferredis the range from about 15 psig to about 1000 psig.

[0044] The following examples merely illustrate the invention. Thoseskilled in the art will recognize many variations that are within thespirit of the invention and scope of the claims.

EXAMPLE 1

[0045] Preparation of a Pentacyclic Diketone

[0046] The procedure of Mehta et al. (J. Am. Chem. Soc. 108 (1986) at3451) is generally used.

[0047] Freshly cracked cyclopentadiene (10 g, 0.15 mol) in toluene (10mL) is added in one portion to an ice-cooled solution of p-benzoquinone(16.2 g, 0.15 mol) in toluene (200 mL). The mixture is stirred at roomtemperature for 1 h, and solvent is removed under reduced pressure. Thesolid residue is recrystallized from petroleum ether to give the desiredDiels-Alder adduct.

[0048] The Diels-Alder adduct (about 26 g) is dissolved innitrogen-purged ethyl acetate (750 mL), and the mixture is irradiatedwith a Hanowia 450-W medium-pressure mercury vapor lamp in a quartzimmersion well through a Pyrex filter for 45 min. Solvent removal andcrystallization gives the desired pentacyclic diketone 7.

EXAMPLE 2

[0049] Thermal [2+2] Cycloreversion to a Bis(enone)

[0050] Mehta's procedure is used to make the bis(enone), 11. Thus, aportion of 7 from Example 1 (2.0 g) is sublimed (130° C., 0.3 mm)through a quartz column that has been preheated to 530° C. (The column(1.5×30 cm) is connected to a vacuum line and provided with a collectionflask and liquid nitrogen trap. The quartz tube is wrapped with anichrome heating wire and asbestos insulation.) The pyrolyzed productfrom the collection flask is purified by washing it through a column ofsilica gel using hexane/ethyl acetate (8:2). Removal of solvent givesthe desired bis(enone) 11.

EXAMPLE 3

[0051] Two-Step Conversion of Bis(enone) to a Triquinane Diene

[0052] The method of Hutchins et al. (J. Org. Chem. 40 (1975) 923) isgenerally followed. Bis(enone) 11 (1.9 g, 11 mmol) andp-toluene-sulfonulhydrazine (4.2 g, 24 mmol, 2.2 eq.) in absoluteethanol (10 mL) are heated on a steam bath for about 30 min. Coolinggives a crystalline product, which is recrystallized from ethanol.

[0053] The tosylhydrazone product is combined with sodiumcyanoboro-hydride (2.75 g, 44 mmol) and 2 mg of Bromocresol Green in 1:1dimethylformamide-sulfolane (70 mL). The mixture is heated to 105° C.Concentrated HCl is added cautiously dropwise until the pH is <3.8 asindicated by a color change from blue to tan. About 25 mL of cyclohexaneare added, and the reaction mixture is heated with stirring for 1 h.Additional indicator and concentrated HCl are added to keep the pH below3.8, and heating continues for 1.5 h. The solution is diluted with water(100 mL), and the layers are separated. The aqueous phase is extractedwith cyclohexane (3×50 mL), and the combined cyclohexane layers arewashed with water, dried, and concentrated. The expected product isdiene 12.

EXAMPLE 4

[0054] Two-Step Conversion of Bis(enone) to a Triquinane Diene

[0055] The method of Hutchins et al. is used to make the tosylhydrazonefrom bis(enone) 11 as shown in Example 3.

[0056] The method of Kabalka et al. is then used to make the diene.Thus, the tosylhydrazone product (2.0 g, about 4 mmol) is dissolved inchloroform (10 mL) at 0° C. Catecholborane (0.53 g, 4.4 mmol) is added,and the mixture is stirred for 2 h. Sodium acetate trihydrate (12 mmol,1.6 g) is added, and the mixture is refluxed gently for 1 h. Aftertypical workup, silica gel chromatography is used to separate thedesired material from polar by-products. The expected product is diene12.

EXAMPLE 5

[0057] One-Step Conversion of Bis(enone) to Triquinane Diene

[0058] The method of Daley, Jr. (J. Org. Chem. 52 (1987) 1984) isgenerally used. Thus, bis(enone) 11 (1.9 g, 11 mmol), boron trifluorideetherate (3.6 mL, 29 mmol), and triethylsilane (4.6 mL, 29 mmol) arecombined and heated at 80-95° C. for 2 h. After cooling, the mixture iscombined with water (15 mL) and extracted into ether (3×20 mL). Thecombined organic layers are washed with 10% aq. NaHCO₃ and saturated aq.NaCl. After drying (MgSO₄), the mixture is concentrated. The expectedproduct is diene 8.

EXAMPLE 6

[0059] Preparation of a Zirconium Complex

[0060] A sample of diene 8 (90 mg, 0.6 mmol) is dissolved in hexanes (50mL) at room temperature, and potassium t-butoxide (136 mg, 1.22 mmol) isadded, followed by n-butyllithium (0.61 mL of 2M solution in pentane,1.22 mmol). The reaction mixture is stirred at room temperature for 20h. Solids are separated and washed several times with hexanes to removelithium t-butoxide from the desired dianion salt. Zirconiumtetrachloride (135 mg, 0.59 mmol) is added to a slurry of the dianionsalt in hexanes (40 mL), and the mixture is stirred at room temperaturefor 16 h. The expected product is the zirconium complex (10, M=Zr,X=Cl).

EXAMPLE 7

[0061] Supporting the Complex

[0062] Methyl alumoxane (30% PMAO solution in toluene, product ofAlbemarle, 1.07 mL) is added slowly to silica (Davison 948 silica,calcined at 250° C. for 4 h prior to use, 2.2 g), and the mixture isstirred at room temperature for 15 min. Separately, a portion of thecomplex prepared in Example 6 (20 mg) is dissolved in 30% PMAO solution(2.14 mL). This mixture is added using an incipient-wetness technique tothe PMAO-treated silica to give a free-flowing solid suitable for use asan olefin polymerization catalyst.

EXAMPLE 8

[0063] Ethylene Polymerization

[0064] A two-liter reactor is charged with isobutane (900 mL) and ascavenging amount of triisobutylaluminum (1.5 mL of 1 M solution inhexanes, 1.5 mmol). The reactor is heated to 70° C. and pressurized withethylene to 350 psig. A slurry of the silica-supported catalyst fromExample 7 (1.0 g) in isobutane (100 mL) is injected into the reactor tostart the polymerization. Ethylene is supplied on demand at 350 psig,and the reaction proceeds at 70° C. for 0.5 h. The reactor is thenvented. Polyethylene is the expected product.

EXAMPLE 9

[0065] Copolymerization of Ethylene with 1-Butene

[0066] A two-liter reactor is charged with hydrogen (20 psig from a 300mL vessel) followed by isobutane (800 mL), 1-butene (100 mL), andtriisobutylaluminum (1.5 mL of 1 M solution in hexanes, 1.5 mmol). Thereactor is heated to 70° C. and pressurized with ethylene to 350 psig. Aslurry of the silica-supported catalyst from Example 7 (1.0 g) inisobutane (100 mL) is injected into the reactor to start thepolymerization. Ethylene is supplied on demand at 350 psig, and thereaction proceeds at 70° C. for 0.5 h. The reactor is then vented.Polyethylene is the expected product.

[0067] The preceding examples are meant only as illustrations. Thefollowing claims define the invention.

I claim:
 1. A catalyst system useful for polymerizing olefins whichcomprises an activator and an organometallic complex, wherein thecomplex comprises a Group 3-10 transition metal and at least onechelating, dianionic triquinane ligand that is pi-bonded to the metal.2. The catalyst system of claim 1 wherein the activator is selected fromthe group consisting of alkyl alumoxanes, alkylaluminum compounds,aluminoboronates, organoboranes, ionic borates, and ionic aluminates. 3.The catalyst system of claim 1 wherein the complex includes a Group 4transition metal.
 4. The catalyst system of claim 1 wherein the complexincludes a Group 8-10 transition metal.
 5. The catalyst system of claim1 wherein the triquinane ligand has the structure:

in which each R is independently hydrogen, halide, or C₁-C₃₀hydrocarbyl.
 6. The catalyst system of claim 5 wherein each R is ahydrogen.
 7. The catalyst system of claim 1 wherein the complex has thestructure:

in which M is a Group 4 transition metal and each X is a halide.
 8. Thecatalyst system of claim 1 wherein the triquinane ligand is preparedfrom cyclopentadiene and p-benzoquinone in a sequence of steps thatincludes tandem Diels-Alder, photochemical [2+2] cycloaddition, and[2+2] thermal cycloreversion reactions.
 9. A method for preparing anorganometallic complex useful for olefin polymerization, said methodcomprising: (a) converting a pentacyclic diketone to a triquinane diene;(b) doubly deprotonating the triquinane diene to produce a triquinanedianion; and (c) reacting the dianion with a transition metal source togive an organometallic complex that incorporates a chelating, dianionictriquinane ligand.
 10. The method of claim 9 wherein the pentacyclicdiketone is produced by (a) reacting a cyclopentadiene and ap-benzoquinone to produce a Diels-Alder adduct; and (b) photolyzing theDiels-Alder adduct to effect a [2+2] cycloaddition reaction to give thepentacyclic diketone.
 11. The method of claim 9 wherein step (a) isaccomplished by first heating the pentacyclic diketone to cause a [2+2]cycloreversion reaction to give a cis,syn,cis-triquinane bis(enone),followed by conversion of the bis(enone) to the triquinane diene. 12.The method of claim 11 wherein the bis(enone) is converted to thetriquinane diene by (a) reacting the bis(enone) with an arylhydrazine toproduce an arylhydrazone; and (b) reducing the arylhydrazone to thediene by reacting it with an alkali metal cyanoborohydride orcatecholborane.
 13. The method of claim 11 wherein the bis(enone) isconverted to the triquinane diene by reacting it with atriakylhydrosilane in the presence of a Lewis acid.
 14. The method ofclaim 9 wherein step (a) is accomplished by first converting thepentacyclic diketone to a pentacyclic hydrocarbon by reducing thecarbonyl groups to methylene groups, and then heating the pentacyclichydrocarbon to cause a [2+2] cycloreversion reaction to give thetriquinane diene.
 15. The method of claim 9 wherein the pentacyclicdiketone is homologated by reacting it with diazomethane prior toconversion to the triquinane diene.
 16. A method for preparing anorganometallic complex useful for olefin polymerization, said methodcomprising: (a) reacting a cyclopentadiene and a p-benzoquinone toproduce a Diels-Alder adduct; (b) photolyzing the Diels-Alder adduct toeffect a [2+2] cyclo-addition reaction to give a pentacyclic diketone;(c) converting the pentacyclic diketone to a triquinane diene; (d)doubly deprotonating the triquinane diene to produce a triquinanedianion; and (e) reacting the dianion with a transition metal source togive an organometallic complex that incorporates a chelating, dianionictriquinane ligand.
 17. The method of claim 16 wherein the Diels-Alderadduct is produced from cyclopentadiene and p-benzoquinone.
 18. Aprocess which comprises polymerizing an olefin in the presence of thecatalyst system of claim
 1. 19. A process which comprises polymerizingethylene with at least one α-olefin in the presence of the catalystsystem of claim 1.